A second mysterious, robotic space plane was launched into orbit by the U.S. Air Force today, after the first craft safely returned to Earth late last year following a secretive months-long mission and speculation about its potential military or intelligence uses.

The second Boeing-built X-37B Orbital Test Vehicle, or OTV, left Cape Canaveral, Fla., at 2:46 p.m. PT, atop an Atlas V rocket, Boeing said.
The present mission is scheduled to last about 270 days, but the Air Force said that might be extended. The first craft stayed in orbit 224 days.